The best way I have found is to contain the dog to a specific area of the car, and then line or protect that area so there is no contact between the dog and unprotected surfaces of the car.
Of course that is easy to implement with a Westie that sheds very little (and is happy to nap quietly in his bed while traveling), as opposed to a Lab or Husky that is in a constant state of throwing off hair into the environment.
If your dog travels in the back, plastic is your friend. Hair seems to magnetically bond with carpet, so cover all carpeted surfaces in the back with some kind of liner.